1. Field of the Invention
This invention relates to charge coupled semiconductor devices (CCD) and in particular to an amplifier constructed from charge coupled devices.
2. Prior Art
W. S. Boyle and G. E. Smith describe the basic concept of charge coupled semiconductor devices in an article published in the April, 1970 Bell System Technical Journal, page 587, entitled "Charge Coupled Semiconductor Devices".
As described by Boyle and Smith, a charge coupled device consists of a metal-insulator -semiconductor (MIS) structure in which minority carriers are stored in a "spatially defined depletion region", also called a "potential well", at the surface of the semiconductor material. The charge is moved along the surface by moving the potential minimum. A paper on page 593 of the same Bell System Technical Journal by Amelio et al., entitled "Experimental Verification of the Charge Coupled Device Concept" describes experiments carried out to demonstrate the feasibility of the charge coupled device concept.
As discussed by Boyle and Smith, charge coupled devices are potentially useful as shift registers, delay lines, and in two dimensions, as imaging or display devices.
Kim and Snow, in patent application Ser. No. 136,087 entitled "Charge Coupled Devices with Continuous Resistor Electrode" filed Apr. 21, 1971, and assigned to Fairchild Camera and Instrument Corporation, the assignee of this application, disclose a charge coupled device wherein the spaced electrodes are formed on the surface of an insulating layer in turn placed over the semiconductor substrate. Each electrode is spaced from adjacent electrodes by resistive material.
In one embodiment, the electrodes are formed with metal and a resistive material is placed between the electrodes. In another embodiment, the electrodes are formed from heavily-doped polycrystalline silicon while the resistive material comprises substantially intrinsic polycrystalline silicon. The Kim and Snow structure increases the allowable spacing between electrodes without decreasing the efficiency with which charge is tranferred from beneath one electrode to beneath an adjacent electrode.